I have spent some time working the numbers and am thinking of the design outlined below for a new (as far as I know) wild cat. From my preliminary numbers, it looks like the cartridge may fill a nitch for 1k shooters, as well as hunters like myself and possibly (though I'm not sure of the feed implications of such a design and am looking for input here too) for the AR shooters.

I focused on 4 major design constraints:

1)Case capacity approximately half way or slightly more, between the .260 Rem and 6.5x.284 Winchester

2)Has to be able to function through a short action repeater, using most 139 to 142 grain bullets seated as close as possible to the junction of the neck and shoulder. If any bullet types needed to encroach on the powder space, this was to be minimized as much as possible.

3)Needs to be formable from a case that was readily available, and of very good quality

4)Utilizes a long neck to allow for greater variety of bullet weights and configurations in the 123 to 142 range if desired, while still maintaining at least .25 grip on the bullet with all desired bullets (also potential minor benefits on minimizing throat erosion)

Here are the rough numbers I come up with on paper. Any feedback would be extremely appreciated as I suspect most all up here have more experience than myself on this sort of thing plus I'm doing on-paper calculations as my copy of Load From a Disk won't arrive for several days from Texas. I'm referring to it as the 6.5 SLiC (Slick Little Cartrige) and it's based on a shortened WSM case, necks turned and reamed. I plan on using the same WSM body taper as well.

... so the usable volume would be 5.8 grains less than the ever-popular 6.5x.284 Winchester, with the hopes it will tread quite closely on the velocities as the case is shorter, fatter, & hopefully more efficient; it's also anticipated that having a capacity of about 6 less grains will improve the barrel life 200 to 500 rounds. Unlike the 6.5x.284, it should function well through a short action even with the longer bullets not being seated down into the boiler room. Lastly, it should give noticeably better velocities than the .260 Rem or even the .260 Rem Ackley Improved.

Any feedback would be much appreciated - I'm thinking of ordering up reamers in the next couple of days so suggestions on improvements would be great! Thanks everyone for your time.

I just remembered one last thing... was considering a outside neck diameter of .293 similar to the 6.5x.284 Winchester and substantially neck turning&reaming accordingly - any feedback on that dimension also would be great -thanks again!

Not trying to burst your bubble, cause I love tinkering with stuff to make it perform better. But IMHO that is a lot of work, custom reamer (no problem) custom dies, 200-300 bucks plus the wait to get them made, forming, trimming, and turning brass and after all is said and done you are still playing second fiddle to what is arguably one of the most inherantly accurate rounds out there and with absolutely top notch brass, (Lapua) the 6.5x284.But if your are like me you won't listen to anybody else anyway, so go for it and keep us posted as to how it goes.Dave

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Definitely understand Dave, not looking for something to replace the 6.5x.284... just a cartridge that will do better velocity-wise with 140-class bullets than the 260 Rem Ackley Improved when that cartridge is set up to operate in a short action (which requires the bullet to be seated down into the powder space.) Make sense?

I'm looking for something beltless that will get somewhere approaching the 6.5x.284 velocity-wise when using 140s (though undoubtedly lower, hopefully lowever velocity by less than 70 to 80 fps), and to do so in in a package that must function through a short action repeater. This is my primary driving force - how do do this with 140s in a short action repeater. Thoughts?

It's good that you've decided -up front, to turn the necks. This will be needed as forming down the WSM case will greatly thicken the brass. A WSSM case is basically a formed down WSM case. That's why the WSSM brass is ungodly thick, and a total failure in Winchester's form. Maybe they really don't know what they're doing..

Also, I cannot stress enough, that you must have the brass in-hand to properly fill out a reamer sheet. In the pic I added my 6.5WSSM, and you might notice it is actually a different diameter(.551) than it's shown in any available drawing. If I had chosen .557(based on .555) for my reamer, .200 from the base, I would not get 5 firings from my brass. I went .553 and have well over 20reloads so far.

I wonder if you would REALLY be able to use it in a short action. I suppose it depends on which action and the loading port length. I use a long action BAT with my 6.5WSSM, and there is not alot of extra room. Reason being, 140gr bullets a VERY long. You will end up 1/4" shorter than a 260. Is a 260 a short action cartridge?
There is also the action diameter to consider. WSM/WSSM factory actions are larger in diameter, and I went with a magnum BAT action. They need to be larger diameter to have enough BARREL STEEL around the chamber. Otherwise the brass will grow like no tomorrow.

You may or may not gain overall compared to going 6.5-284, as it will be alot of work.
My 6.5WSSM is not better than any 260..
On the otherhand, it's no worse, and your 6.5Slic will be a fine cartridge I'm sure.
Just a matter of commiting to a larger boltface..
Good luck to ya, & have fun with it.

Scott good luck with your cartrige. In my humble opinion, I think your trying to fill a gap that dosen't exist. My 26" barreled 260AI will push 140 grain bullets to 2925 fps. I've gotten 5 reloads on the brass I'm using and the pockets are still tight. I don't know what top velocities are out of the 6.5-284 with 140's but most book listings run between 2900 and 3000 fps. I'm feeding out of a factory savage box with no ill effects. Your cost to develop this cartrige may in the end prove fruitless.

Scott good luck with your cartrige. In my humble opinion, I think your trying to fill a gap that dosen't exist. My 26" barreled 260AI will push 140 grain bullets to 2925 fps. I've gotten 5 reloads on the brass I'm using and the pockets are still tight. I don't know what top velocities are out of the 6.5-284 with 140's but most book listings run between 2900 and 3000 fps. I'm feeding out of a factory savage box with no ill effects. Your cost to develop this cartrige may in the end prove fruitless.

Cowboy and Mike! Big thanks goes to both of you. Cowboy - those numbers sounds very enticing - can you tell me if you are using a short or long action though? That would make a very big difference to me as I had assumed the 140s would be so deeply seated in the case on a short action that those types of velocity numbers would not be attainable. In a long action that sounds about what I'd expected though. Thanks!

Mike, thanks a ton for the words of wisdom on the brass life and the time spent on the drawings! I will go study them entranced to see what epiphanies I get

Scott, I ran out to the shop to look up my load, 140gr a-max, 49.5gr H4831sc, cci200, OAL of 2.870". I could seat them longer but this is where they feed reliably and shoot well. Short action, 3 groove 8 twist.